1. Field of the Invention
The present invention relates to a housing shell for an in-the-ear hearing aid and to a method and apparatus for manufacturing the same by making a positive ear mold and from that a negative mold for the housing shell including providing a venting channel therein.
2. Description of the Prior Art
Among the in-the-ear hearing aids, one differentiates between custom-made devices which are either mainly carried in the outer ear as conch devices and merely project into the auditory canal with an ear-matching piece (Siemens Hinweise zur Anfertigung von Ohrpasstuecken fuer Im-Ohr-Geraete SIRETTINA PA 3801, Order No. MH 170/1418, published 1980) or which are placed for the most part in the auditory canal as auditory canal devices, as known from the German Utility Model 84 36 783 and the European application 0,248,955. Also known in the art are module-in-the-ear devices, as known from the European application 0,206,213 and the German application 36 16 648, which are composed of standard module hearing aids, which are integrated in shells or otoplastics manufactured according to the individual mold of the patient.
In addition to a sound entry opening to the microphone and a sound channel from the receiver through a sound exit/trumpet to the eardrum of the person wearing the hearing aid, in-the-ear hearing aids are provided with a further opening and a channel which enables ventilation of the auditory canal that is actually closed by the device. Apart from pressure compensation, this additional channel, also called a vent, can also serve for the manipulation of the frequency response of the hearing aid depending on how it is laid out (course, diameter boring), and it can be adapted to the hearing loss of the person wearing the hearing aid.
For the manufacturing of an in-the-ear device with a vent channel, a conventional procedure provides that the acoustical engineer active in the field of hearing aids, for example, creates a positive mold of the ear of the hearing-impaired person. This mold, particularly on that side not facing the ear drum, the distal end of the mold, is planarly cut, provided with a mold release, expediently the entire ear mold is dipped in wax, and with the application of a matching shell, a negative of the ear mold is cast. After the ear mold is taken out of the negative form, the form is filled with plastic material (e.g. polymethyl methacrylate, known by the name Acryl PMMA) for the generation of a housing shell for the hearing aid. After a brief polymerization time, the excess plastic material is poured out of the negative form. After the casting or extrusion/injection molding, the negative form with the housing shell located therein is placed in a pressure pot, for example, and over a time interval of approximately 10 minutes, the plastic is hardened (polymerized). Subsequently, the housing shell is taken out of the negative form.
The hardened blank part of the housing shell that is taken out of the negative form is cleared proximally and distally from excess plastic material as indicated in FIG. 5 by the lines c--c and e--e. This occurs by way of abrading or sawing or milling and polishing. Furthermore, an opening is cleared (drilled, milled open) at the proximal end of the housing shell blank. Subsequently, the shell is polished.
For the creation of a ventilation channel or vent, with time-consuming work that requires great care, a groove is applied into the inner wall of the housing shell over the entire length of the shell by means of a milling tool starting at the distal end or the proximal end. In this groove, a silicon hose encasing a core of solder wire is placed and fastened at the shell from the exterior. Now, a mixture of the plastic material for the shell is prepared and applied on the sleeve of the silicon hose with a tool (spatula) such that inside the housing shell the hose is covered and embedded over its entire extent. For the hardening of the masking material for the silicon hose, the blank of the housing shell is once again placed, for example, in a pressure pot for a certain period of time. Subsequently, the excess masking material is milled off and polished off in order to create space in the housing shell for the integration of the components of the hearing aid. Thereby, it must be observed and checked that the channel which results after the silicon hose is pulled out has a closed jacket/sleeve.
In the following, the blank of the housing shell is ground/cut off in the conch area (distal end) and in the area of the auditory canal (proximal end) to the desired shape of the housing shell. Finally, a face plate can be applied at the distal end and an end plate or cerumen cap or such at the proximal end. Thereby, the inlet and outlet openings of the vent are to be drilled if necessary. If the vent ends before the cerumen cap in the area of the proximal end, an opening must be drilled into the wall of the housing shell.